This invention relates to a system for the collection and extraction of gases entrained in a fluid, and more particularly, hydrocarbon gases in the return flow drilling mud material of an oil or gas exploration well.
There is a demand for apparatus to collect gases emitted from and extract gases entrained in fluid and slurry materials. For example, gases entrained in the return flow material discharged from an oil or gas exploration well. This return flow material is generally in the form of a mud stream and is usually referred to as drilling mud. Collection, extraction and analysis of drilling mud gases can be used to indicate the hydrocarbon content in the well return flow material which, in turn, provides the basis for an assessment of the formation and any indications that the well drilling has hit a producing zone. In an oil and gas well, generally the primary hydrocarbon gas of interest is methane gas. Thus, information relating to the methane gas content of the well return flow material is the information that is usually of most interest. Although, under certain drilling conditions, there is also interest in information relating to some of the other hydrocarbons that may be present in the well return flow material.
The gases obtained from the return flow material discharged from the oil or gas exploration well are sampled for analysis. A gas collection, extraction device provided for this purpose is generally referred to as a gas trap. The gas trap apparatus is typically positioned in a xe2x80x9cShaker Boxxe2x80x9d or xe2x80x9cPossum Bellyxe2x80x9d of a xe2x80x9cShaker Tankxe2x80x9d into which the well return material is directed when it exits the well bore. Generally, the gas trap provides the collected, extracted gases to a sample tube extending from the gas trap to the sample analysis equipment. The sample tube typically has a small diameter and the collected gas sample is transported in the sample tube to sample analysis equipment on a continuous basis.
The current state of the art drilling mud gas sample collection, extraction systems have several problems that cause such systems to require high maintenance costs and attention. Current gas trap apparatus provides a canister with an electric motor mounted on top, which drives a centrifugal impeller housed centrally within the canister. The canister has a plate on the bottom with a small hole in the centre that acts as an inlet for the drilling mud. Another hole is provided in the side of the canister that forms an outlet for the drilling mud to be expelled from. This arrangement is designed both to pump mud through the gas trap sample canister and to agitate the mud contained within the sample canister sufficiently to permit entrained gases to be released. The gases are released from the return drilling fluid well mud stream as gas bubbles and are evacuated from the sample canister via a sample outlet, which couples to a sample tube.
Current gas traps are quite heavy, usually weighing 70 lbs. or more making the devices relatively heavy and, consequently, onerous to install, operate and maintain. Generally, the gas traps are attached to the shaker box and disposed inside of the shaker box, positioned at a particular depth in the drilling mud flowing through the shaker box. Typically, the apparatus for attaching the gas trap to the shaker box includes a bracket that permits up and down adjustment of the gas trap to allow the gas trap to be positioned at the correct depth in the drilling fluid. Positioning the gas trap at the prescribed or optimum depth in the drilling fluid is very important with the current design of gas traps. Any variation from the optimum depth causes the gas trap to change the amount of drilling mud it will pass in a given period of time as well as causing it to liberate more or less entrained gases from the drilling mud in that same given period of time. Furthermore, if the level of the drilling mud rises too high, drilling mud will be drawn into and through the sample tube by the sample pump toward the sample analyzer causing contamination of the equipment. Depending on the amount of drilling mud drawn into the sample tube, the sample handling, conditioning and analysis systems can all become contaminated with the drilling mud. At a minimum, drawing drilling mud into the sample tube will cause contamination that will require maintenance intervention and may necessitate replacement of the sample tube. In operation, most shaker boxes will experience a change in drilling mud level as the mass flow quantity of drilling mud changes or as the density and viscosity of the drilling mud changes. Drilling mud level changes in the shaker box can also occur as a result of the rig crew making adjustments to the shaker box itself.
Current oil and gas well drilling gas traps require operational maintenance and attention to operate in harsh winter environments. For example, the collected gas sample is typically delivered to analysis equipment that often is distances of hundreds of feet from the gas trap. A sample tube effects delivery of the sample, which is subject to freezing in the winter. Consequently, the sample is dehumidified to avoid freeze-up in the sample tube. Dehumidification apparatus typically includes a glycol dryer that the sample is bubbled through. The moisture removed from the sample causes the vessel holding the glycol to become full, requiring replacement of the glycol to rejuvenate the apparatus. Another, dryer apparatus generally found is a solid desiccant, for example calcium chloride, to further dry the sample. The solid desiccant will require replacement, often several times per day, to maintain operation of the dehumidifier systems. An example of such type of systems is described in U.S. Pat. No. 4,565,086 to Orr.
U.S. Pat. No. 5,199,509 to Wright for a controlled gas trap system provides a gas trap forming a sample chamber having an inlet and outlet both submersed in the fluid to be sampled. Disposed within the gas trap is a rotating agitator and a vent to admit substantially gas-free air into the housing and a means to draw off the gas evolved from the mud. To provide for varying mud levels, the apparatus of Wright relies on the rotation of agitator to maintain a constant mud level within the sample chamber.
U.S. Pat. No. 5,648,603 to Hansen describes a method and apparatus for stabilizing a quantitative measurement gas trap used in a drilling operation. The method involves providing a known quantity of standard gas for injection to the trap in which the gas stream is evolved, for example Ethylene, Isobutylene and Nitrous Oxide.
It is desirable to have a drilling mud gas sample collection, extraction system that is operable over a range of drilling mud levels within the sampled flow stream, for example, in a shaker box.
It is desirable to have a drilling mud gas sample collection, extraction system that operates consistently over a wide range of ambient temperatures, including freezing winter temperatures.
It is desirable to have a drilling mud gas sample collection, extraction system that operates consistently over a wide range of drilling mud viscosity.
It is desirable to have a drilling mud gas sample collection, extraction system that operates with little or no frequent operator maintenance or intervention.
The invention provides a gas trap assembly to recover sample gases from fluids having pneumatic motor driven agitator blade rotatably disposed within a gas sample collection canister. To enable operation of the pneumatic motor in winter conditions, the pneumatic motor compressed air supply has an air dryer to dry the air supply to a dew point below minus 40 degrees Celsius. The compressed air treatment system is housed in a heated environment to prevent the water extracted from the air from freezing up.
For operation in winter environments, a heater heats the motor compressed air supply. The heated compressed air is delivered to the gas trap to power the gas trap pneumatic motor. Before going to the motor at the gas trap, the heated compressed air is passed through a heat exchanger on the gas trap to warm the gas trap apparatus to ensure the sample gas is maintained at a temperature above its dew point and prevent freezing. Sample gas recovered from the fluid is supplied to a sample tube for transport to analysis equipment. In the preferred embodiment, the sample tube is bundled together with the air supply tube inside an insulated jacket. This arrangement transfers heat from the heated compressed air supply tube to the sample tube to keep the sample gas warm until it arrives at the analyzer equipment.
Within the gas trap, changing mud levels in the fluid flow in which the gas trap is disposed are controlled to a set or predetermined level using compressed air. To maintain the drilling fluid mud level at a consistent level within the gas trap, a two-chamber configuration is employed comprising a sample canister forming the first chamber and a bubbler enclosure or canister forming a second chamber. Compressed air is supplied in common to both chambers, consequently, the bubbler enclosure regulates the pressure within the sample canister to keep the mud level within it constant. The bubbler enclosure is sealed at the top and has an air exit port opening at the bottom at the level or point where the mud level in the sample canister is desired to be. The exit port opening at the bottom of the bubbler enclosure may be provided by cutting off the bubbler enclosure at the desired length. In operation of the gas trap, pressurized air is supplied to bubbler enclosure. The chamber formed by the bubbler enclosure is in common air communication with the sample chamber of sample canister through a passageway equalizing the pressure in the two chambers.
To operate the gas trap, the amount of air supplied to the bubbler enclosure is slightly greater than the amount of sample gas drawn from the chamber formed by the sample canister. Therefore, the bubbler enclosure will always be bubbling air out of the bottom as long as it is under the surface of the mud. The cavities formed by the bubbler enclosure and the sample canister are in communication with each other, consequently, the mud level maintained by the air pressure within the bubbler enclosure causes the mud level inside the sample canister to be at the same level. Variations in the drilling mud level exterior to the gas trap in the shaker box can rise a great deal without having any effect on the level of the drilling mud within the sample chamber of the gas trap. With this arrangement, the gas trap is prevented from xe2x80x9cfloodingxe2x80x9d, that is, the condition where drilling mud is sucked up into the sample tube. In the event that main air pressure is lost, it would be possible for the gas sample extraction pump to suck the drilling mud into the sample tube following main air pressure loss.
In a preferred embodiment, the sample canister provides baffles projecting into the sample cavity formed by the sample canister. The baffles prevent or reduce mud fluids from entering into the sample tube.
To prevent or reduce contamination of the sample tube and to remove condensed moisture that may be collected in the sample tube, the sample tube can be purged when the flow of sample gas through the sample tube falls below a lower threshold. To purge the sample tube, pressurized air is supplied to the sample tube causing a gas flow through the sample tube that is the reverse of the sample gas flow. Preferably, the reverse flow pressurized air is supplied at higher flow rates and pressures than that of the sample gas.
In one of its aspects, the invention provides an apparatus to recover gases from a fluid that includes a sample canister submersible in a fluid. The sample canister forms a sample cavity and has a fluid ingress port and a fluid egress port to provide a path for the flow of fluid through the sample cavity of the canister. A sample extraction port is exterior to the sample canister and in communication with the sample cavity. A bubbler enclosure is attached to the sample canister and has an exit port at a predetermined location in relation to the sample container and a supply port adapted to receive a supply of pressurized gas. A passage extends between the sample canister and the bubbler enclosure to provide a path for communication of pressurized gas from the supply port to the sample cavity of the sample canister. When the sample canister is submersed in a fluid, a supply of pressurized gas to the inlet port of the bubbler enclosure will result in a level of fluid within the sample cavity of the sample canister that is correspondingly set by the exit port location of the bubbler enclosure.
In another of its aspects, the invention provides an apparatus to recover gases from a fluid that has a sample container adapted for submersion in a fluid. The sample container forms sample cavity therein and includes a fluid ingress port and a fluid egress port to provide a path for the flow of fluid through the sample cavity of the container. A sample extraction port is exterior to the sample container and in communication with the sample cavity. Agitator means is rotatably disposed within the sample cavity of the sample canister and a motor drives the agitator. A bubbler enclosure is attached to the sample container and has an exit port at a predetermined location in relation to the sample container. A supply port is adapted to receive a supply of pressurized gas into the bubbler enclosure and a passage extends between the bubbler enclosure and sample container to provide a path for communication of pressurized gas from the supply port to the sample cavity of the sample container.
In yet another of its aspects, the invention provides apparatus to recover gases from a fluid operable in freezing conditions including a sample container adapted for submersion in a fluid. The sample container forms a sample cavity therein and a fluid ingress port and a fluid egress port to provide a path for the flow of fluid through the sample cavity. A sample extraction port is exterior to the sample container and in communication with the sample cavity. An agitator is rotatably disposed within the sample cavity of the sample canister and motor means is provided to drive the agitator. A bubbler enclosure is attached to the sample container and has an exit port at a predetermined location in relation to the sample container. A supply port is adapted to receive a supply of pressurized gas and a passage extending between the sample container and the bubbler enclosure provides a path for communication of pressurized gas from the supply port to the sample cavity and the bubbler enclosure. The apparatus also includes a source of pressurized air and a heater to heat the pressurized air. A heat exchanger block is disposed on a frame supporting the sample canister and the bubbler enclosure to recover heat from the pressurized air.
And in yet another of its aspects, the invention provides apparatus operable in freezing conditions to warm a gas recovered from a well drilling return flow fluid. A sample tube receives a gas recovered from a well drilling return flow fluid and a second tube is adapted to receive a source of heated air that axially coextends with said sample tube to facilitate heat exchange between them.
In another aspect, the invention provides apparatus to facilitate transport in freezing conditions of a sample gas recovered from a fluid that includes at least two longitudinal co-extending hoses forming a common surface there along. The hoses are adapted to facilitate heat exchange between them. One hose is for transport of a sample gas and the other hose is for transport of heated air. A sheath surrounds the co-extending hoses providing the capability to transfer heat energy is from the heated air hose to the sample gas hose.
In yet another of its aspects, the invention provides apparatus to indicate the relative viscosity of a fluid including an agitator adapted for rotatable placement in a viscose fluid. A pneumatic motor is provided to effect rotation of the agitator. A variable valve controls the supply of compressed air to the pneumatic motor means in response to a control signal produced by a controller. A sensor produces rotation signalling representative of the rotation of the agitator for the controller. The controller operates to maintain a substantially constant rate of rotation of said agitator by varying the control signal with relative changes in fluid viscosity.
In another of its aspects, the invention provides a self cleaning apparatus to recover gases from a fluid including a sample container submersible in a fluid. The sample container forms a sample cavity and has a fluid ingress port and a fluid egress port to provide a path for the flow of fluid through the sample cavity of the sample container. A sample extraction port is exterior to the sample container and in communication with said sample cavity. A means to draw a flow of gas through the sample extraction port causes a flow of gas through the sample extraction port in a supply direction. The invention has a flow valve operable to connect a source of compressed air to the sample extraction port to effect a flow of compressed air through the sample extraction port in a direction reversed to the supply direction. Activation means effects operation of the flow valve. The activation means operates the flow valve when the flow of gas through the sample extraction port is too low or periodically.
The preferred embodiments of the invention will now be described with reference to the attached drawings, which are briefly described as follows: